The present invention relates to a system for detecting the transmission ratio in an infinitely variable belt-drive transmission for a vehicle during driving. European Patent Application Publication No. 0005565 discloses a control system for an infinitely variable transmission.
The infinitely variable belt-drive transmission comprises an endless belt running over a primary pulley and a secondary pulley. Each pulley comprises a movable conical disc which is axially moved by a fluid operated servo device so as to vary the running diameter of the belt on the pulley depending on driving conditions. The system is provided with an oil pressure regulator value and a transmission ratio control valve. Each valve comprises a spool to control the oil pressure by shifting the spool.
The primary pulley has a Pitot pressure generating device for producing Pitot pressure dependent on engine speed. The Pitot pressure is applied to one axial end of the spool of each valve to urge the spools to shift. On the other hand, the actual transmission ratio is detected by the axial position of the movable conical disc of the primary pulley which represents the running diameter of the belt on the primary pulley. A conventional transmission ratio detecting system comprises a rod which is moved dependent on the axial movement of the movable conical disc and a link for transmitting the movement of the rod to the other axial end of the spool of the pressure regulator valve. Such a mechanism is complicated in construction.